International Space Station crew will do Saturday spacewalk to address leak

By Greg Botelho and Laura Smith-Spark, CNN

Updated 11:57 AM ET, Sat May 11, 2013

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International Space Station – The crew of the space shuttle Atlantis took this picture of the International Space Station after leaving it in July 2011. Atlantis was the last shuttle to visit the station, which was first launched in 1998 and built by a partnership of 16 nations.

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International Space Station – The crew of the space shuttle Endeavour initiates the station's first assembly sequence in 1998. The International Space Station includes several large modules, each launched separately and connected in space by astronauts.

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International Space Station – The Zarya control module, on the left with the solar panels, floats above Earth with its newly attached Unity module after the first assembly sequence in December 1998.

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International Space Station – The first crew of the International Space Station, seen on board in December 2000. From the left are cosmonaut Yuri P. Gidzenko, astronaut William M. Shepherd and cosmonaut Sergei K. Krikalev.

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International Space Station – The Endeavour crew installs the first set of U.S. solar arrays on the station in 2000.

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International Space Station – In March 2001, a space shuttle delivered the station's second crew and brought the first one home. It also brought Leonardo, the station's first Multi-Purpose Logistics Module, to the station. Leonardo carried supplies and equipment.

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International Space Station – In September 2006, the space shuttle Atlantis docked with the space station, delivering solar wings and a new truss.

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International Space Station – The space shuttle Discovery leaves the space station in March 2008 after its crew successfully delivered and installed the Japanese-built Kibo lab.

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International Space Station – The unmanned SpaceX Dragon spacecraft connects to the space station in May 2012. It was the first private spacecraft to successfully reach an orbiting space station.

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International Space Station – An unmanned Russian cargo craft disconnects from the space station in April 2013. The station relies heavily on ships to bring up supplies.

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International Space Station – Commander Koichi Wakata of the Japan Aerospace Exploration Agency peers out of the space station's Cupola observatory on April 27. The Cupola is a dome-shaped module that allows station crew members to observe and guide activities outside the station.

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International Space Station – A Russian Soyuz spacecraft is docked with the space station on May 5. Since the U.S. shuttle program ended in 2011, all crew members are ferried to and from the space station on Russian rockets.

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International Space Station – A Soyuz spacecraft is seen on May 13 as it lands in Kazakhstan with Wakata and other members of the his Expedition 39 crew.

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Story highlights

NASA says the spacewalk will start Saturday morning and last 6½ hours

Ammonia is leaking from a cooling loop on a solar array on the space station

It was spotted Thursday, and officials have worked round-the-clock since to devise a plan

"This type of event is what the years of training were for," the orbiter's commander writes

Two International Space Station crew members will head out Saturday morning for a spacewalk to address an ammonia leak in the orbiter's cooling system, an emergency that forced NASA officials to work round-the-clock to hatch a plan.

First detected early Thursday morning, the leak was causing ammonia to enter space -- which could be seen in the form of "flakes of snow" -- at a rate of 5 pounds per day, said Mike Suffredini, NASA's space station program manager. Ammonia is used to cool each of the solar arrays that provide electricity to station systems.

The discovery spurred teams at NASA, over a busy 24-hour stretch, to go into "a full-court press to understand what the failure is" and how to address it, NASA flight director Norm Knight said at a Friday news conference.

The space station's six-man crew is in "good spirits" in anticipation of the spacewalk, added Knight, a sentiment echoed by a tweet Friday afternoon by its commander.

"This type of event is what the years of training were for," wrote Cmdr. Chris Hadfield of Canada. "A happy, busy crew, working hard, loving life in space."

Hours earlier, Hadfield wrote on Twitter that his crew was planning for a Saturday spacewalk to be conducted by NASA astronauts Chris Cassidy and Tom Marshburn.

Hadfield -- who is with the Canadian Space Agency -- spent Friday preparing for his role as choreographer of the spacewalk, while Cassidy and Marshburn worked in an airlock to check out the spacesuits they will wear in space, among other tasks.

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Cassidy and Marshburn have done two spacewalks apiece, working together both times in 2009 while on a space shuttle Endeavour mission to the space station.

"Since the crew is prepared and our ops team is ready to go, we're going to try to get them outside," said Suffredini.

Scheduled to wake up at 2 a.m. ET, the astronauts will begin their formal preparations about 1 hour and 15 minutes later, Knight said. A hatch will open around 8:15 a.m., sometime after which Cassidy and Marshburn will start moving along a truss the 150 feet out to the site of the leak on the space station's U.S. segment.

Once there, Knight explained, the astronauts will do a "visual inspection" of the leak -- the location of which space agency officials have "narrowed down" thanks to imagery, though Suffredini notes any cracks may be "very, very small." They will also check and possibly replace a pump controller box on the truss, which NASA explains is "the oldest component of the station's backbone."

The entire walk is expected to take about 6½ hours.

The space station's crew, which also includes three Russian cosmonauts, is not in danger from the leak, NASA has said. Moreover, the agency has said the rest of the orbiter is otherwise operating normally.

The leak is in a cooling loop in a solar array that has leaked before. NASA said crew members tried to fix a leak in November. It's unclear whether this is the same leak or a new one.

The ammonia coolant for the power channel, one of eight used to supply electricity to the station, is likely to run out by late Friday morning and it will be shut down, NASA said.

"It is a serious situation, but between crew and experts on the ground, it appears to have been stabilized," Hadfield tweeted Thursday.

Three crew members, Cassidy and Russian cosmonauts Alexander Misurkin and Pavel Vinogradov, will remain on the space station when the others leave.

They will be joined at the end of the month by three new crew members: NASA astronaut Karen Nyberg, Russian cosmonaut Fiyodor Yurchikhin and European Space Agency astronaut Luca Parmitano, who are due to launch aboard a Russian Soyuz spacecraft on May 28.